OBJECTIVE： To investigate and analyze the use of TCM decoction pieces not in conformity with the Chinese Pharmacopoeia and influential factors， and to investigate its rationality on theoretically and clinically. METHODS： Stratified random sampling was adopted to select 1 200 TCM decoction pieces prescriptions from outpatient pharmacy of the hospital during Jul.-Dec. 2015 and perform a retrospective and descriptive analysis on general information， incompatibility， excess defined dose and influential factors， etc. RESULTS： 1 200 prescriptions were collected， involving 378 ingredients which appeared 17 826 times. Male occupied 45.92％ and female occupied 54.08％. （14.86±5.01） ingredients were prescribed in each prescription averagely； the amount of each dose was（243.73±100.84）g； the amount of each ingredient was（16.41±8.57）g. Incompatibility may be occurred in 2 970 ingredients， involving 1 093 prescriptions； incompatibility couplet medicines appeared in same prescription 18 times， accounting for 1.50％ of total prescriptions and 0.20％ of ingredient times. There were 353 kinds of drugs with litmit standard， involving utilization ratio of excess defined dose was 56.64％ by ingredient times， 94.62％ by types and 98.83％ by prescriptions. The proportion of excess defined dose in each prescription was （56.58±19.56）％ averagely， and utilization ratio of excess defined dose was increased as the increase of drug types； deviation degree of average amount for each type was（40.19±50.37）％. There was significant difference in utilization ratio of excess defined dose among different gender and age groups， and senior physicians were easy to use drugs over the defined dose. Utilization ratio of excess defined dose had no obvious regularity in term of efficacy classification. More large excess defined dose was， mere rare excess defined dose was. CONCLUSIONS： Incompatibility is not common in TCM prescriptions of the hospital， but excess defined dose is serious and universal； influential factors are numerous and complex. The use of TCM decoction pieces not in conformity with Chinese Pharmacopoeia is in a way acceptable in the sense of theory and practice. Practitioners are advised to view it in a dialectical way in their daily clinical practice， in order to ensure safety and effectiveness at the same time and to coordinate the practice with the theory for them to progress together.